A driveline of a vehicle may operate in a speed control mode from time to time when driver demand torque is at a low level. By operating in a speed control mode, the driveline may avoid operating at conditions where it may be difficult to control driveline torque or conditions where driveline noise and vibration may be greater than is desired. A hybrid vehicle may operate with an internal combustion engine and an electric motor while in a driveline speed control mode. Because the electric motor has a higher torque bandwidth than the engine, it may be operated in the driveline speed control mode to smooth driveline torque pulsations that may be related to cylinder firing events in the internal combustion engine. However, there may be select operating conditions where it may be more difficult to maintain a desired driveline speed in the driveline speed control mode even with the motor's higher torque bandwidth.
The inventors herein have recognized the above-mentioned issue and have developed a driveline operating method, comprising: reducing a torque output range of authority of a motor to a non-zero value in a driveline operating in a speed control mode in response to a battery state of charge exceeding a threshold level.
By reducing a torque output range of authority of the motor to a non-zero value, it may be possible to provide the technical result of improved driveline speed control even during conditions where a high state of battery charge precludes battery charging via the motor. For example, when battery state of charge is not at a high state, the motor may operate within its full range of torque (e.g., from maximum positive motor torque to maximum negative motor torque at the present motor speed) to maintain driveline speed at a desired driveline speed. However, if the battery state of charge is at a higher state of charge, motor torque may be limited to a range less than the full range of torque so that driveline speed control may be improved even when the battery may accept lower rate of charging. In one example, the motor torque may be limited based on driveline disconnect clutch inertia and motor inertia. The driveline inertia may be effectively electronically reduced so that actions taken by an engine speed controller may improve driveline speed control.
The present description may provide several advantages. For example, the approach may provide improve driveline speed control, especially when a vehicle battery is at a high state of charge. Additionally, the approach may be applied during varying operating conditions where the desired driveline speed may not be constant. Further, the approach may improve battery life by reducing the battery rate of charge when the battery is operating at a higher state of charge.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.